1. Field of the Invention
The invention herein relates to riser sleeves, hot tops, ladle liners and similar objects for use in the casting of molten metal. More particularly, it relates to an insulating refractory fiber composition from which such articles for use in the casting of molten metals (especially molten ferrous metals) can be formed.
In the casting of molten metals there are steps in which the molten metal must be held in receptacles for conveying, risering, and the like. In each of these applications it is required to minimize the cooling of the molten metal and the possibilities of the metal attacking the receptacle structure. Therefore riser sleeves, ladle liners, and similar articles are formed of refractory materials and utilized as described below.
In the casting of molten metal it is common practice to provide a riser or reservoir communicating with the actual mold cavity. As the metal within the mold cavity cools it contracts, and the riser serves as an additional molten metal supply to maintain a full quantity of metal within the mold cavity. Since the riser itself also solidifies on cooling means must be provided to keep metal in the riser molten for as long as possible in order to allow the riser to serve its function as a reservoir and source of molten metal. It has become common practice to line the interior surface of the riser hole with either an insulating material or an exothermic material. These linings are generally referred to as "riser sleeves" or "hot tops." The insulating type of riser sleeve serves to retain the heat of the molten metal in the riser and thus delay the cooling and solidification of the riser. The exothermic type of riser sleeve contains material which will burn when placed in contact with the molten metal and thus provides an external heating source to the riser. The riser sleeves of the present invention are of the insulating type.
Similarly, the ladles used to convey molten metal must provide insulating or exothermic liners to minimize heat loss and cooling of the metal. In the case of the ladle liner, it is also important that the attack of the metal on the ladle structure itself be minimized. The ladle liner should be as resistant as possible to attack of the molten metal, so that the ladle need not require frequent relining.
Riser sleeves, ladle liners, and the like intended for use with molten ferrous metals must be able to withstand temperatures and thermal shocks greater than those used with the casting of nonferrous metals. This is because the melting points of the ferrous metals are generally considerably higher than the melting points of many common nonferrous metals such as aluminum, copper, lead, zinc and the like as well as that of several common alloys such as bronzes and brasses. Such used herein, "ferrous metals" means those predominately consisitng of iron, nickel, chromium and related elements such as the various cast irons and steels. In practice the invention herein will find its principal use in the casting of steel and steel alloys.
2. Description of the Prior Art
Since molten metal casting is an old and well studied art there is a large number of patents dealing with refractory compositions, configurations and methods of manufacture. Those which may be considered to have more than average pertinence to the present invention include U.S. Pat. Nos. 3,077,413; 3,092,247; 3,100,734; 3,321,171; 3,344,838; 3,352,743; 3,456,914; 3,478,999; and 3,558,591, and British Pat. No. 894,056. All these patents deal with insulating compositions which contain refractory materials including refractory fiber.